1. Field of the Invention
The present invention relates to a phase control switch apparatus for controlling open/close (break/make) timings of a breaker connected to the power transmission system to thereby protect reactive loads or reactor components such as transformers, shunt reactors, capacitor banks (CB) and the like connected to the electric power system against an exciting rush current, a transient surge current or the like which takes place upon opening/closing of the breaker and which exerts adverse influences to the reactive load. More specifically, the present invention is concerned with a switchgear apparatus equipped with a phase-based break/make controller designed for suppressing the transient currents mentioned above to a possible minimum by controlling optimally the timings at which the breaker is to be closed.
2. Description of Related Art
Switchgear such as the breaker is generally equipped with a break/make timing control apparatus for the purpose of suppressing the exciting rush current, transient surge voltage or the like which occurs upon closing of the breaker by controlling the closing time point or timing of the breaker by taking into account the arcing time and like influential factors.
For having better understanding of the present invention, description will first be made in some detail of the conventional phase control switch apparatus (break/make timing control apparatus) known heretofore. FIG. 24 of the accompanying drawings shows a structure of a hitherto known break/make control apparatus for a breaker typifying the switchgear together with the standard waveforms of R-, S- and T-phase supply voltages in breaker contact closing operation as well as operation timings of the breaker. Parenthetically, this apparatus is disclosed in Japanese. Patent Application Laid-Open No. 156820/1991 (JP-A-3-156820).
Referring to FIG. 24, reference numeral 10 denotes generally a transformer connected or wired in a Y-connection with a neutral point being connected to the ground potential, and numeral 50 denotes generally a breaker having arc-extinction chambers 52a, 52b and 52c within which contacts are disposed. For making it possible to perform open/close (break/make) operations for these contacts independently of one another, the contacts are equipped with respective actuator devices 54a, 54b and 54c. Further, in FIG. 24, reference characters 72a, 72b and 72c denote voltage measuring devices designed for measuring R-, S- and T-phase supply voltages, respectively, and numeral 80 denotes generally a phase-based break/make controller provided for the breaker 50. The phase-based break/make controller 80 is comprised of a reference phase detecting unit 82 and an arithmetic processing/operation control unit 81.
Description will now turn to operation of the breaker and the phase control switch apparatus.
The R-, S- and T-phase supply voltages are measured by the voltage measuring devices 72a, 72b and 72c, respectively, the output signals thereof being transmitted to a reference phase detecting unit 82 incorporated in the phase-based break/make controller 80. The reference phase detecting unit 82 is designed for detecting the zero-point cycles of the R-, S- and T-phase supply voltages, respectively, to thereby determine the voltage-zero point which is to serve as the standard or reference time point Tstandard.
Upon reception of make (close) command for closing the breaker 50, the arithmetic processing/operation control unit 81 constituting a part of the phase-based break/make controller 80 determines arithmetically a closing or making operation time tclose and a pre-arcing time tprearc as predicted from the ambient temperature of the actuator devices, operating forces thereof and voltage measurement data, whereon the predicted closing operation time tclose is subtracted from a time period intervening between the preset R-, S- and T-phase closing (making) target time point Ttarget (e.g. electrical angle of 90xc2x0 for voltage peak) and the reference time point Tstandard while adding the pre-arcing time tprearc, to thereby determine an operation synchronizing time period tcont.
Upon lapse of the operation synchronizing time period tcont from the reference time point Tstandard, the arithmetic processing/operation control unit 81 of the phase-based break/make controller 80 supplies the close or make signals to the individual actuator devices 54a, 54b and 54c, respectively, to thereby control the closing or making operations for the contacts disposed within the arc-extinction chambers 52a, 52b and 52c independently of one another so that these contacts can be closed independently each at a predetermined electrical angle which allows the switching surge phenomenon or event (i.e., surge current occurring upon closing) to be suppressed to a minimum.
Such closing or making operation of the breaker 50 performed at the voltage peak through the control procedure or sequence described above is adopted in many practical applications for closing various load apparatuses and equipment such as exemplified by transformers or shunt reactors in the state in which substantially no residual magnetic flux exists and which is thus favorable to suppression or avoidance of the switching surge event as well as for closing capacitor banks and transmission lines in the no-load state in which the switching surge phenomenon or event can be suppressed by closing the breaker 50 at the voltage-zero point.
As is apparent from the above, the closing control for transformers, shunt reactors or the like has conventionally been performed in the state where substantially no residual magnetic flux exists, allowing thus the switching surge taking place transiently upon contact closing to be suppressed by closing the breaker 50 at a voltage peak point. In reality, however, in case the residual magnetic flux is present in the core of the transformer or shunt reactor, great difficulty is encountered in operating the breaker 50 at the closing time point which is optimal for suppressing the switching surge event, giving rise to a problem.
In the light of the state of the art described above, it is an object of the present invention to provide a phase control switch apparatus which is capable of suppressing transient switching surge phenomena by operating or actuating the breaker at an optimum making or closing time point determined on the basis of the residual magnetic flux predicted for each phase of the transformer, the shunt reactor or the like reactive load notwithstanding of existence of the magnetic flux in the core thereof. Parenthetically, it should be pointed out that such making or closing control of the breaker which can suppress the transient surge and the like phenomena is generally considered to be difficult in the case where the residual magnetic fluxes exist in the core of the transformer, the shunt reactor or the like reactive load.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to an aspect of the present invention a phase control switch apparatus which includes a breaker connected to a reactive load connected to a three-phase electric power system in A-connection or alternatively in Y-connection with a neutral point being connected directly to the ground or alternatively not connected to the ground, the breaker being designed to break a fault current and a load current flowing through the reactive load or make the reactive load closed to the three-phase electric power system for excitation thereof, a voltage measuring means for measuring phase voltages on a phase-by-phase basis, a current measuring means for measuring inter-contact currents at an output side of the breaker, an actuating means for effectuating open/close operations of contacts of the breaker independently on a phase-by-phase basis, a temperature measuring means disposed in the vicinity of the actuating means, a reference phase detecting means for detecting driving pressures and control voltages of the actuating means for the breaker on a phase-by-phase basis, the reference phase detecting means being so designed as to respond to a brake/make command issued to the breaker to thereby predict waveforms of phase voltages, respectively, upon closing of the breaker as well as phases and periodical zero points of waveforms of phase currents, respectively, upon opening of the breaker on the basis of voltage values and current values measured by the voltage measuring means and the current measuring means, respectively, a residual magnetic flux predicting means for storing breaking time points of the phase contacts of the breaker, respectively, and positive/negative polarities of individual phase currents immediately before breaking in a preceding breaking operation to thereby predict residual magnetic fluxes in the individual phases of the reactive load on the basis of the contents as stored, an optimal closing time point predicting means for predicting upon closing of individual phase contacts of the breaker an optimal closing electrical angle for each of the phases on the basis of the residual magnetic fluxes of the reactive load in the individual phases as predicted by the residual magnetic flux predicting means so that surges occurring upon closing of the breaker contacts can be suppressed each to a minimum, and a contact closing operation starting means for validating contact closing operations of the breaker so that the phase contacts of the breaker can be closed at the electrical angles, respectively, which are predicted and set by the optimal closing time point predicting means.
In a preferred mode for carrying out the invention, the residual magnetic flux predicting means may be so designed that on the precondition that the residual magnetic flux in a first phase broken firstly in the preceding break operation of the three-phase electric power system by the breaker is zero, when a second phase to be broken succeedingly is broken with a phase lag of 60xc2x0 (⅙ cycle) relative to the first broken phase and when the first phase current is of positive polarity immediately before the breakage thereof with the polarity of the second phase current immediately before the breakage thereof being negative, decision is then made such that the residual magnetic flux in the second broken phase is negative (e.g. residual magnetic flux of xe2x88x9290%), while when the third phase current to be broken finally is broken with a phase lag of 60xc2x0 (⅙ cycle) relative to the second phase current and when the second phase current is of negative polarity immediately before the breakage thereof with the polarity of the third phase current immediately before the breakage thereof being positive, decision is then made such that the residual magnetic flux in the third broken phase is positive (e.g. residual magnetic flux of 90%), whereas on the precondition that the residual magnetic flux in the first phase broken firstly in the preceding break operation of the three-phase electric power system by the breaker is zero, when the second phase current to be broken succeedingly is broken with a phase lag of 60xc2x0 (⅙ cycle) relative to the first phase current and when the first phase current is of negative polarity immediately before the breakage thereof with the polarity of the second phase current immediately before the breakage thereof being positive, then decision is made such that the residual magnetic flux in the second broken phase is positive (e.g. residual magnetic flux of 90%), while when the third phase current to be broken finally is broken with a phase lag of 60xc2x0 (⅙ cycle) relative to the second phase current and when the second phase current is of positive polarity immediately before the breakage thereof with the polarity of the third phase current immediately before the breakage thereof being negative, decision is then made such that the residual magnetic flux in the third broken phase is negative (e.g. residual magnetic flux of xe2x88x9290%).
In another preferred mode for carrying out the invention, the residual magnetic flux predicting means may be so designed that on the precondition that the residual magnetic flux in the first phase broken firstly in the preceding break operation of the three-phase electric power system is zero, when the second phase to be broken succeedingly is broken with a phase lag of 120xc2x0 (⅓ cycle) relative to the first phase and when the first phase current is of positive polarity immediately before the breakage thereof with the polarity of the second phase current immediately before the breakage thereof being positive, decision is then made such that the residual magnetic flux in the second broken phase is negative (e.g. residual magnetic flux of xe2x88x9290%), while when the third phase current to be broken finally is broken with a phase lag of 120xc2x0 (⅓ cycle) relative to the second phase current and when the second phase current is of positive polarity immediately before the breakage thereof with the polarity of the third phase current immediately before the breakage thereof being positive, decision is then made such that the residual magnetic flux in the third broken phase is positive (e.g. residual magnetic flux is 90%), whereas on the precondition that the residual magnetic flux in the first phase broken firstly in the preceding break operation is zero, when the second phase current to be broken succeedingly is broken with a phase lag of 120xc2x0 (⅓ cycle) relative to the first phase current and when the first phase current is of negative polarity immediately before the breakage thereof with the polarity of the second phase current immediately before the breakage thereof being negative, decision is then made such that the polarity of the residual magnetic flux in the second broken phase is positive (e.g. residual magnetic flux is 90%), while when the third phase current to be broken finally is broken with a phase lag of 120xc2x0 (⅓ cycle) relative to the second phase current and when the second phase current is of negative polarity immediately before the breakage thereof with the polarity of the third phase current immediately before the breakage thereof being negative, decision is then made such that the residual magnetic flux in the third broken phase is negative (e.g. residual magnetic flux of xe2x88x9290%).
In yet another preferred mode for carrying out the invention, the residual magnetic flux predicting means may be so designed as to be previously inputted with absolute values of residual magnetic fluxes of positive and negative polarities, respectively.
In still another preferred mode for carrying out the invention, the residual magnetic flux predicting means may be so designed that the absolute values of the residual magnetic fluxes of the positive and negative polarities are set each at a value within a range of 80% to 90% and that when a value of a rush current occurring upon closing operation of the breaker is greater than an expected value, the preset values of the residual fluxes of the positive and negative polarities are increased or decreased so that the rush current can approximate the expected value.
In a further preferred mode for carrying out the invention, the optimal closing time point predicting means may be so designed that on the basis of such results of prediction performed by the residual magnetic flux predicting means for each phase of the reactive load that the residual magnetic fluxes in the phases are zero, negative and positive, respectively, the optimal closing time point predicting means predicts contact closing time points (electrical angles) for the phases such that surges occurring upon closing of the phases can be suppressed to a minimum by setting the closing time points for the first and second phases to be closed, respectively, in terms of corresponding electrical angles on the basis of the respective residual magnetic fluxes, while setting the closing time point for the third phase to be closed at a same time point as the closing time points of the first and second phases or alternatively at a later time point.
In a yet further preferred mode for carrying out the invention, the optimal closing time point predicting means may be so designed that on the basis of such results of prediction performed by the residual magnetic flux predicting means for each phase of the reactive load connected in Y-connection with a neutral point connected directly to the ground that the residual magnetic flux of the first broken phase is zero, the residual magnetic flux of the second broken phase is negative and the residual magnetic flux of the third broken phase is positive, the optimal closing time point predicting means predicts contact closing time points (electrical angles) for the phases, respectively, such that surges occurring upon closing for the phases can be suppressed to a minimum by setting the phase for which the residual magnetic flux is zero (first broken phase) as the first phase to be closed, while setting the phase for which the residual magnetic flux is positive as the second phase to be closed and setting the phase for which the residual magnetic flux is negative as the third phase to be closed, wherein the closing time point for the first phase to be closed for which the residual magnetic flux is zero is set in the vicinity of an electrical angle of 90 degrees (voltage peak) or alternatively at an electrical angle within a range of 60 to 120 degrees (voltage peak), while the closing time point for the second phase to be closed for which the residual magnetic flux is positive is set in the vicinity of an electrical angle of 75 degrees or alternatively at an electrical angle within a range of 60 to 90 degrees, and wherein the closing time point for the third phase to be closed for which the residual magnetic flux is negative is set at a same time point as the closing time point of the second phase or alternatively at a later time point.
In a still further preferred mode for carrying out the invention, the optimal closing time point predicting means should preferably be so designed that on the basis of such results of prediction performed by the residual magnetic flux predicting means for each phase of the reactive load connected in Y-connection with a neutral point connected directly to the ground that the residual magnetic flux of the first broken phase is zero, the residual magnetic flux of the second broken phase is negative and the residual magnetic flux of the third broken phase is positive, the optimal closing time point predicting means predicts contact closing time points (electrical angles) for the phases, respectively, such that surges occurring upon closing of the phases can be suppressed to a minimum by setting the phase for which the residual magnetic flux is zero (first broken phase) as the first phase to be closed, while setting the phase for which the residual magnetic flux is negative as the second phase to be closed and setting the phase for which the residual magnetic flux is positive as the third phase to be closed, wherein the closing time point for the first phase to be closed for which the residual magnetic flux is zero is set in the vicinity of an electrical angle of 90 degrees (voltage peak) or alternatively in the vicinity of an electrical angle within a range of 60 to 120 degrees (voltage peak), while the closing time point for the second phase to be closed for which the residual magnetic flux is negative is set at an electrical angle of 315 degrees or alternatively at an electrical angle within a range of 300 to 330 degrees, and wherein the closing time point for the third phase to be closed for which the residual magnetic flux is positive is set at a same time point as the closing time point of the second phase or alternatively at a later time point.
In another mode for carrying out the invention, the optimal closing time point predicting means should preferably be so designed that on the basis of such results of prediction performed by the residual magnetic flux predicting means for each phase of the reactive load connected in Y-connection with a neutral point connected directly to the ground that the residual magnetic flux of the first broken phase is zero, the residual magnetic flux of the second broken phase is positive and the residual magnetic flux of the third broken phase is negative, the optimal closing time point predicting means predicts contact closing time points (electrical angles) for the phases, respectively, such that surges occurring upon closing of the phases can be suppressed to a minimum by setting the phase for which the residual magnetic flux is zero as the first phase to be closed, while setting the phase for which the residual magnetic flux is positive as the second phase to be closed and setting the phase for which the residual magnetic flux is negative as the third phase to be closed, wherein the closing time point for the first phase to be closed for which the residual magnetic flux is zero is set in the vicinity of an electrical angle of 90 degrees (voltage peak) or alternatively at an electrical angle within a range of 60 to 120 degrees, while the closing time point for the second phase to be closed for which the residual magnetic flux is positive is set in the vicinity of an electrical angle of 280 degrees or alternatively at an electrical angle within a range of 260 to 300 degrees, and wherein the closing time point for the third phase to be closed for which the residual magnetic flux is negative is set at a same time point as the closing time point of the second phase or alternatively at a later time point.
In yet another mode for carrying out the invention, the optimal closing time point predicting means should preferably be so designed that on the basis of such results of prediction performed by the residual magnetic flux predicting means for each phase of the reactive load connected in Y-connection with a neutral point connected directly to the ground that the residual magnetic flux of the first broken phase is zero, the residual magnetic flux of the second broken phase is positive and the residual magnetic flux of the third broken phase is negative, the optimal closing time point predicting means predicts contact closing time points (electrical angles) for the phases, respectively, such that surges occurring upon closing of the phases can be suppressed to a minimum by setting the phase for which the residual magnetic flux is zero as the first phase to be closed, while setting the phase for which the residual magnetic flux is negative as the second phase to be closed and setting the phase for which the residual magnetic flux is positive as the third phase to be closed, wherein the closing time point for the first phase to be closed for which the residual magnetic flux is zero is set in the vicinity of an electrical angle of 90 degrees (voltage peak) or alternatively at an electrical angle within a range of 60 to 120 degrees (voltage peak), while the closing time point for the second phase to be closed for which the residual magnetic flux is negative is set in the vicinity of an electrical angle of 40 degrees or alternatively at an electrical angle within a range of 20 to 60 degrees, and wherein the closing time point for the third phase to be closed for which the residual magnetic flux is positive is set at a same time point as the closing time point of the second phase or alternatively at a later time point.
By virtue of the arrangements of the phase control switch apparatus described above, the contacts of the breaker 50 can be closed at the optimal timings by taking into account the residual magnetic fluxes in the individual phases determined on the basis of the predicted residual fluxes in the transformer 10, the shunt reactor or the like reactive load, whereby the transient surge or the like phenomena taking place upon breaker contact closing operation can be suppressed to a minimum advantageously.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.